It is known in an electrophotographic copying machine to mount one or the other of an image carrying drum and a developing unit so that it may be removed from the copying machine through movement in the longitudinal direction of the image carrying drum. Either the drum or the developing unit is designed to be removable to simplify assembly of the machine during manufacturing and to make it easier to repair and maintain the machine.
In an electrophotographic copying machine, the developing unit is mounted in a frame at a position adjacent to the image carrying drum. The developing unit is provided with a developing roller for carrying developer to the developing zone so that an electrostatic latent image formed on the image carrying drum may be developed to form a toner image. A matching roller is mounted on the shaft of the developing roller and is brought into engagement with the image carrying drum to establish a predetermined gap between the photosensitive drum and the developing roller.
Running the steps of removing the developing unit from the body of the copying machine for maintenance, there arises a problem of damaging the surface of the image carrying drum by the matching roller engaging the drum. In high speed electrophotographic copying machines, the thickness of the ear of the developer formed on the surface of the developing sleeve of the developing unit, that is, the gap between the outer surface of the image carrying drum and that of the developing sleeve, is set to a value of about 0.5 1.00 mm. Thus, even for machines that have no matching roller, the surface of the developing sleeve of the developing unit often contacts the surface of the image carrying drum at the time of mounting or dismounting the developing unit on, or from, the machine frame and damages the expensive image carrying drum. Another problem is that the ear of the developer magnetically attracted to the surface of the developing sleeve rubs against the surface of the drum and the toner drops outside the machine causing environmental pollution.
In order to solve the above problems, a downwardly inclined rail has been arranged within the machine frame and the developing unit is mounted on, or dismounted from, the machine frame along the rail.
This structure is not without problems in that the equipment surrounding the copying machine must be removed when mounting or dismounting the developing unit, requiring increased labor and time for maintenance and control of the machine as well as during assembly during manufacture.